1. Field of the Invention
The present invention relates to a valve device for use in a reaction gas passage of a fuel cell system, and more particularly to a valve device for bypassing a humidifier disposed in a reaction gas passage of a fuel cell system to supply a reaction gas from a heat radiator to the cathodes of fuel cells.
2. Description of the Related Art
Solid polymer membrane fuel cell devices have a stack of cells each comprising a solid polymer electrolyte membrane sandwiched between an anode and a cathode that are disposed one on each side of the solid polymer electrolyte membrane. For operating such a stack of cells, hydrogen is supplied as a fuel to the anode and air is supplied as an oxidizing agent to the cathode. Hydrogen ions are generated at the anode by a catalytic reaction, and move through the solid polymer electrolyte membrane to the cathode where the hydrogen ions and oxygen in the air cause an electrochemical reaction to generate electric power.
If the temperature of the air is low or the fuel cell system has not reached a necessary temperature and the air does not reach a sufficient temperature even when the air is compressed by a heat radiator, then the air needs to bypass a humidifier and to be directly supplied to the cathode. Specifically, a bypass passage is provided parallel to the humidifier, and the air compressed by the heat radiator is either supplied to the humidifier or supplied through the bypass passage to the cathode depending on the temperature of the air. The flow of the air is switched between the humidifier and the bypass passage by a valve with a rotary solenoid incorporated therein (see Japanese Laid-Open Patent Publication No. 2001-250716).
The rotary solenoid disclosed in Japanese laid-open patent publication No. 2001-250716 has a bobbin with a coil wound therearound and a rotor comprising a permanent magnet oriented substantially perpendicularly to the axis of the bobbin. When an electric current flows through the coil, the rotary solenoid is energized to turn the rotor and a shaft which is coupled substantially centrally to the rotor together.
The valve with the rotary solenoid incorporated therein is disposed in the bypass passage. When the rotor is turned, the bypass passage is switched into and out of communication, thereby switching the flow of the air between humidifier and the bypass passage.
In a fuel cell system having the valve including the rotary solenoid disclosed in Japanese Laid-Open Patent Publication No. 2001-250716, the valve is disposed in the bypass passage, and no valve is disposed in a main passage which interconnects the heat radiator and the humidifier. If the temperature of the air is low or the fuel cell system has not reached a necessary temperature and the air does not reach a sufficient temperature even when the air is compressed by a heat radiator, then when the compressed air is supplied from the heat radiator through the bypass passage to the cathode, a portion of the compressed air is also supplied through the main passage to the humidifier, which supplies humidified air to the cathode. Consequently, the fuel cell system is unable to achieve an optimum temperature which matches the characteristics of the solid polymer electrolyte membrane, and has its electric generation efficiency lowered.